1. Field of the Invention
The present invention relates to intraocular lenses and, more particularly, to lenses having stable bendable haptics defining a circular flexible fixation member when implanted.
2. Description of the Prior Art
The visual rehabilitation of a patient afflicted with cataract has been a controversial topic within the cognoscente for decades. To understand the concept of intraocular lens implants, one must first have an intimate knowledge of the anatomy of the eye and the characteristics of a cataract. Light enters through the cornea of an eye. The cornea is a clear transparent tissue that serves as a window which allows entry of light and provides some amount of focusing capability. The light traverses the anterior chamber and penetrates the crystalline lens. The lens acts as a major focusing element for the light. The light, after being focused by the lens, continues on its path through the vitreous and impinges upon the retina. The impinging light is transformed into electrical impulses by the reaction of layers of complex specialized retinal nerves. The nerves transmit the electrical impulses to the brain which translates them into visual sensations.
The word cataract refers to a clouding of the normally clear lens. The causes of cataract need not be reviewed except to say that senile cataract is an extremely common affliction of patients over the age of sixty and leads to varying amounts of significant visual disability. When a cataract is present, the light normally penetrating the crystalline lens for focusing is impaired by the clouded areas. When the cataract becomes severe enough, the only treatment available is surgical removal of the cataract which is equivalent to surgical removal of the crystalline lens. At the present time, there are no medicinal cures for most patients afflicted with cataract.
With the surgical removal of the crystalline lens, the resulting eye is deficient in focusing power. In the early years of cataract surgery, this deficiency of focusing power was corrected by using a thick lens held in front of the eye by a spectacle frame. Improvements in visual rehabilitation came with the availability of contact lenses. A contact lens is located on the surface of the cornea and compensates for the deficiency in focusing power.
A third alternative of visual rehabilitation is the use of an intraocular lens implant (IOL). An IOL is a small plastic lens with lens support structures that is inserted into the eye by surgery. The difficulties enumerated above attendant thick lenses and contact lenses are completely eliminated. Moreover, the patient has no sensation of the presence of the IOL and if the implant is successful, the IOL may be in the eye permanently to replace the lost focusing power of the removed crystalline lens. A preferred plastic is polymethyl methacrylate (PMMA) as techniques are now known for molding or otherwise fabricating an IOL from this material.
An intraocular lens falls into one of three broad categories depending upon its position within the eye. An anterior chamber intraocular lens is placed within the anterior chamber in front of the iris. Its fixation is dependent on various styles of loops that are supported in the angles of the anterior chamber, whereby the iris tissue is allowed to move freely. From a technical standpoint, the anterior chamber IOLs are the easiest to implant. The difficulties with prior art anterior chamber IOLs include: (1) deficient manufacturing methods which leave rough edges on the implant and result in chronic irritation (iritis), elevated intraocular pressure (glaucoma) and bleeding from within the anterior chamber (hyphema); (2) the lens support structure is of solid plastic construction, rather than flexible loop construction, which can lead to blockage of the normal aqueous flow within the eye (pupillary block glaucoma); (3) the lack of sufficient flexibility of the support structure leads to difficulties with tenderness on touching of the eye and normal movements during one's daily activities can lead to chronic irritation within the eye; (4) the prior art anterior chamber IOLs have to be matched in size to the patient's eye which increases IOL inventory problems. More importantly, without accurate measurements of the patient's eyes, an inflexible or insufficiently flexible IOL that is too small results in increased movement of the implant that can lead to chronic irritation while an implant that is too large tends to distort the eye, cause discomfort and lead to chronic irritation. The major advantage of an anterior chamber IOL is that it may be used after either intracapsular or extracapsular surgery.
An iris supported IOL is an implant that depends on iris tissue or a combination of iris tissue and capsular tissue for its support. It has significant disadvantages because of its lack of uniplanar design and its constant iris contact.
A posterior chamber IOL is inserted behind the iris to position the lens in the exact anatomical position of the previously removed cataract or crystalline lens. The major disadvantage of prior art posterior chamber IOLs is that the cataract must be removed by extracapsular techniques. The advantages attendant posterior chamber IOLs in general include: (1) fixation at the posterior capsule provides good stability to the eye; (2) as no iris fixation is present, the pupil behaves normally; (3) the implant is uniplanar and therefore is generally easy to insert without damaging other structures; (4) dislocation is rare but if it should occur, the implant does not dislocate anteriorly to damage the cornea; and (5) the patient is visually rehabilitated as nearly as is physiologically possible since the implant is in the exact location as the previously removed crystalline lens.